This article covers the studies on phytoalexins activity of phenolic compounds (cinnamic acids, flavonoids, isoflavonoids, deoxianthocyanins, stilbenes, coumarins, chromones) against fungi and bacteria. The relationship between hydrophilic-lipophilic balance activity is reported. Finally some reports on the preparation of synthetic phytoalexins sharing structural similarities with the natural ones (stilbenes, epi-catechin derivatives), of commercial interest as pesticides, insecticides and fungicides, are revised.